A communication network may communicate information using optical signals transmitted as light pulses. Certain devices of a communication network may include optical modulators that modulate the optical signals. Signals that drive the optical modulators typically should be aligned in time in order to properly modulate the signals. The relative delay between driving signals, however, may change due to, for example, temperature variation or device wear. Known alignment variation monitoring techniques involve using optical filtering or microwave signal processing to monitor drift in the relative delay. These known techniques, however, are not satisfactory in certain situations.